---
title: "pg_aios"
id: view-pg-aios
pg_version: "20devel"
---

<a id="view-pg-aios"></a>

## 53.2. pg_aios

The pg_aios view lists all [Asynchronous I/O](glossary.md#glossary-aio) handles that are currently in-use. An I/O handle is used to reference an I/O operation that is being prepared, executed or is in the process of completing. pg_aios contains one row for each I/O handle. 

This view is mainly useful for developers of PostgreSQL, but may also be useful when tuning PostgreSQL. 

**pg_aios Columns**

| Column Type | Description | 
| --- | --- |
| `pid` `int4` | Process ID of the server process that is issuing this I/O. |
| `io_id` `int4` | Identifier of the I/O handle. Handles are reused once the I/O completed (or if the handle is released before I/O is started). On reuse [pg_aios.`io_generation`](view-pg-aios.md#view-pg-aios-io-generation) is incremented. |
| `io_generation` `int8` | Generation of the I/O handle. |
| `state` `text` | State of the I/O handle: - `HANDED_OUT`, referenced by code but not yet used - `DEFINED`, information necessary for execution is known - `STAGED`, ready for execution - `SUBMITTED`, submitted for execution - `COMPLETED_IO`, finished, but result has not yet been processed - `COMPLETED_SHARED`, shared completion processing completed - `COMPLETED_LOCAL`, backend local completion processing completed |
| `operation` `text` | Operation performed using the I/O handle: - `invalid`, not yet known - `readv`, a vectored read - `writev`, a vectored write |
| `off` `int8` | Offset of the I/O operation. |
| `length` `int8` | Length of the I/O operation. |
| `target` `text` | What kind of object is the I/O targeting: - `smgr`, I/O on relations |
| `handle_data_len` `int2` | Length of the data associated with the I/O operation. For I/O to/from [`shared_buffers` (`integer`)](runtime-config-resource.md#guc-shared-buffers) and [`temp_buffers` (`integer`)](runtime-config-resource.md#guc-temp-buffers), this indicates the number of buffers the I/O is operating on. |
| `raw_result` `int4` | Low-level result of the I/O operation, or NULL if the operation has not yet completed. |
| `result` `text` | High-level result of the I/O operation: - `UNKNOWN` means that the result of the operation is not yet known. - `OK` means the I/O completed successfully. - `PARTIAL` means that the I/O completed without error, but did not process all data. Commonly callers will need to retry and perform the remainder of the work in a separate I/O. - `WARNING` means that the I/O completed without error, but that execution of the IO triggered a warning. E.g. when encountering a corrupted buffer with [`zero_damaged_pages` (`boolean`)](runtime-config-developer.md#guc-zero-damaged-pages) enabled. - `ERROR` means the I/O failed with an error. |
| `target_desc` `text` | Description of what the I/O operation is targeting. |
| `f_sync` `bool` | Flag indicating whether the I/O is executed synchronously. |
| `f_localmem` `bool` | Flag indicating whether the I/O references process local memory. |
| `f_buffered` `bool` | Flag indicating whether the I/O is buffered I/O. |

The pg_aios view is read-only. 

By default, the pg_aios view can be read only by superusers or roles with privileges of the `pg_read_all_stats` role.